Decorative sheet-type covering material such as a sheet vinyl floor or wall covering is frequently made with a substrate comprising sheet-type felt material. The felt generally used for this purpose comprises, as a major component, cellulosic fibers and/or asbestos fibers. Synthetic fibers are sometimes used but are quite expensive. When accessive amounts of synthetic fibers are used, the felt frequently cannot maintain the required dimensional stability and strength characteristics at the elevated temperatures generally used in the manufacture of sheet vinyl flooring. The use of asbestos fibers in such felt is considered to represent a health hazard, while the use of large amounts of cellulosic fibers results in felt which tends to have poor dimensional stability and which is unduly susceptible to biological degradation, especially when installed on or below grade.